From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Tue, 30 Jul 2002 12:38:52 -0400 Subject: Re: [RFC] start_aggressive_readahead Content-Type: text/plain; charset=US-ASCII; format=flowed Mime-Version: 1.0 (Apple Message framework v482) From: Scott Kaplan In-Reply-To: <644994853.1028020916@[10.10.2.3]> Message-Id: Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: "Martin J. Bligh" Cc: Andrew Morton , Rik van Riel , Christoph Hellwig , linux-mm@kvack.org List-ID: -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Tuesday, July 30, 2002, at 12:21 PM, Martin J. Bligh wrote: > Thus I'd contend that either growing or shrinking in straight > response to just a hit/miss rate is not correct. We need to actually > look at the access pattern of the application, surely? I agree. I probably should have made it clear that what I was suggesting wasn't the right way to go about it, but rather an argument against the heuristics that seemed backwards to me. The causes for misses are necessarily as clear cut as you mentioned, as there are a lot of behaviors that are neither fully random nor fully sequential. So, while it is ideal to have some foresight before resizing the window -- some calculation that determines whether or not growth will help or shrinkage will hurt -- it will require the VM system to gather hit distributions. I'm trying to make that happen right now, although for all VM pages, and not for the specific purpose of read-ahead calculations. However, the paper for which I gave a pointer (in a shameless act of self promotion) proposes exactly that: Keeping reference distributions for read-ahead and non-read-ahead pages, and then balancing the two against each other in an attempt to determine what the best read-ahead window size would be given recent reference behavior. There may be simpler, kruftier, and/or more effective versions of what I proposed, but what you said above is, I think, the right idea. Scott -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (Darwin) Comment: For info see http://www.gnupg.org iD8DBQE9RsEf8eFdWQtoOmgRAp+vAJoCF6mUgAI42x6Bac4A2/u+7oZXIwCdHVqZ AQCPlqTF+84udI5xSWqYWas= =swZ6 -----END PGP SIGNATURE----- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/